Parents declare them beautiful, these wailing bundles of wrinkles. But upon arrival, far more than their physical appearance needs work. Indeed, human newborns are the least neurologically developed primates on Earth, their brains a mere 25% developed, compared with about 50% among others in the animal kingdom. Parents might well think of human infants as final-phase fetuses who will spend their first three months — a fourth trimester — crossing the divide between womb and world.
Recent research in neuroscience, biology and developmental science provides a peek into an infant’s world, giving new parents something they have longed for: a user’s manual for newborns.
Human babies arrive with billions of brain cells, or neurons, but little in the way of an internal communication network. Immediately, every interaction with the world — each touch, word, smell, look — helps the baby lay down an infrastructure of dendrites, the branched projections that receive and send signals between neurons.
Fortunately, nature has made sure that the brain stem, central nervous system and other primitive parts of the brain are up and running to keep the heartbeat, circulatory system and other vital functions going. It’s the higher parts of the brain that are influenced by every cuddle, coo and caress, constructing the brain’s architecture and forming a unique personality.
Newborn babies are born completely dependent. Yet they prove remarkably competent. They are ready to build a brain that will soon let them see, speak, learn and love.
What the world sounds like
Grown-ups chattering, siblings nattering, pots and pans clattering: For a while, infants cannot sort through the din of this chaotic world. Still, hearing is the most developed sense at birth. Familiar with the voice heard in muffled form for nine months, an infant recognizes and responds to a mother’s voice first. Apart from that, newborns are not yet ready to assign more or less importance to any one of the countless sounds around them.
But lest anyone think these undifferentiated noises are useless, think again. With an innate skill that would be the envy of a statistics student, newborns are keeping track of probabilities, setting up neural connections in response to the patterns of the words they hear. They are learning where one word ends and another begins long before they utter their first da-da.
Patricia Kuhl, a neuroscientist at the University of Washington and a leading expert on speech development, has found that babies around the world are born with the ability to hear the sound distinctions of every language spoken on Earth. By 10 months of age, and maybe sooner, that ability is lost, pruned away by a brain eager to cultivate what will be needed and get rid of what won’t. Japanese infants, for example, can distinguish the syllables “la†and “ra.†But since those sounds won’t be needed in their homeland, their brains, in a necessary “use-it-or-lose-it†model, prune away the unused neurons. That’s why so many Japanese people, when learning English, have trouble with words like “rice†and “lice.â€
What the world looks like
Vision is the least developed sense at birth. But even brand-new babies are drawn to contrast. What looks like direct eye contact is more likely a baby studying the edge of a face. Something as simple as a brown ceiling fan against a white ceiling might hold the attention for minutes. The fad of buying black-and-white toys and clothing was a response to evidence that infants enjoy contrast. But it was just that: a fad. Any contrasting color scheme will do, and there are plenty available in every home and the great outdoors.
What the world feels like
The newborn’s sense of touch has been influenced for 40 weeks by the warmth of amniotic fluid and the secure confines of the uterus. Swaddling, cuddling and stroking can mimic that comfort as the infant gets used to being in the world. Simple human touch, especially bare skin on bare skin, releases brain chemicals that can calm an infant. (On the other hand, trauma can release neurochemicals that can set a child up for future trouble.)
In what seems like lore from the dark ages of medicine, as recently as 15 years ago, most doctors believed that newborns didn’t feel pain the way adults do. Nurses lanced their heels, drew blood, gave injections; doctors even performed surgery on infants with no pain control. Today, the American Academy of Pediatrics has guidelines to assure that pain control is part of any medical procedure.
What the world smells and tastes like
These two senses, closely linked throughout life, are tied together even in the uterus. Taste and smell filter through amniotic fluid, and infants are born recognizing the taste of mother’s milk and the odor of the first breast secretion before milk comes in, called colostrum. After they’re born, newborns can be finicky, according to research from the European Center for Taste Science in — where else — France. Researchers gave some pregnant women anise, a strong spice. When their infants were presented with the odor, they turned toward it; infants whose mothers did not eat anise turned away from the smell.
Even before babies get their first taste of solid food, cooking aromas influence their future food preferences. So steam those beets and broccoli, throw some blueberries into muffins and heat up a pot of tomato basil soup.
Susan Brink is a freelance medical writer. Her book “The Fourth Trimester: Understanding, Nurturing, and Protecting an Infant Through the First Three Months,†published by University of California Press, was released this spring.
